<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .bxo{
            position: relative;
            width: 178px;
            margin: 100px;
        }
        .con{
            position: absolute;
            top: -40px;
            width: 171px;
            border: 1px solid rgba(0, 0, 0, .2);
            padding: 5px 0;
            box-shadow: 0 2px 4px rgba(0, 0, 0, .2);
            font-size: 18px;
            line-height: 20px;
            color: #333;
            display: none;
        }
        .con::before{
            content: '';
            width: 0;
            height: 0;
            position: absolute;
            top: 28px;
            left: 18px;
            border: 8px solid #000;
            border-style: solid dashed dashed;
            border-color:  #fff transparent  transparent;
        }
    </style>
</head>
<body>
    <div class="bxo">
   <div class="con">111</div>
    <input placeholder="请输入">
</div>
    <script>
        let input = document.querySelector('input');
        let con = document.querySelector('.con');
        input.addEventListener('keyup',function(){
            let result = input.value;
            if(result == ''){
                con.style.display = 'none';
            }else{
                con.style.display = 'block';
                con.textContent = result;
            }
        })
        input.addEventListener('focus',function(){
            if(this.value == ''){
                con.style.display = 'none'
            }else{

                con.style.display = 'block'
            }
        });
        input.addEventListener('blur',function(){
            con.style.display = 'none'
        });
    </script>
</body>
</html>